For removing liquid from masses having great liquid content, it is common to subject the masses to a squeezing in a belt press. In such a press, the material is carried between a pair of endless dewatering belts running substantially parallel to each other through a series of rollers. An example of such squeezing apparatuses are disclosed in U.S. Pat. No. 4,543,880, U.S. Pat. No. 4,557,833 and U.S. Pat. No. 5,113,999. These devices move the material, on belts, through sets of mutually cooperating rollers, in which high transient line pressures are applied on the masses. After this liquid extraction process is completed, the dewatering belts are separated by a pair of rollers rotating in opposite directions. In this manner, the matter is expelled from between the dewatering belts and thus from the belt press for further processing. The sludge matter expelled from the belt filter press is commonly referred to as sludge cake. The sludge cake though dewatered still has a significant water content. It is desirable to remove as much of this water as possible. The present invention is essentially an add-on to a belt press for removing water from sludge cake.